The present invention relates to an atmospheric pressure CVD (Chemical Vapor Deposition) apparatus for cleaning a susceptor for mounting a semiconductor wafer to be processed thereon.
Generally, in an atmospheric pressure CVD apparatus, a heater is set below a susceptor placing a semiconductor wafer thereon. After the semiconductor wafer is heated to a predetermined temperature, a reaction gas blown from a dispersion head set at an upper portion hits the surface of the semiconductor wafer to form a predetermined thin film thereon.
At this time, the thin CVD film is naturally deposited on the exposed surface portion of the upper surface of the susceptor supporting the semiconductor wafer, other than a surface portion mounting the semiconductor wafer thereon. Particles on the film surface become rough with an increase in number of times of CVD processing, and the thin film formed on this susceptor is easily peeled off. The peeled dust attaches to the surface of the semiconductor wafer, producing a defective semiconductor wafer.
When the thin film deposited on the susceptor has a thickness of 20 to 30 .mu.m, this susceptor is exchanged for a cleaned susceptor. However, exchange of the large, high-temperature susceptor must be avoided in consideration of the safety of an operator.
For this reason, this exchange is performed after the heater of the atmospheric pressure CVD apparatus is turned off to cool down the susceptor to almost room temperature. The waiting period for this temperature drop is about 5 to 6 hours, and temperature rise requires a temperature rise period of about 1 hour due to use of the heater. During these waiting periods, the atmospheric pressure CVD apparatus cannot be used. For this reason, the apparatus downtime is about 50 hours per month, decreasing the operating efficiency by about 7%.
Japanese Utility Model Laid-Open No. 61-173133 discloses the prior art of cleaning a susceptor while eliminating wasteful waiting periods for temperature drop and temperature rise, as shown in FIG. 3.
Referring to FIG. 3, an endless belt 45 on which a large number of susceptors 63 are fixed and arrayed at a predetermined interval is reciprocatively, endlessly rotated by a plurality of pulleys 46 rotating in directions indicated by arrows. A semiconductor wafer (not shown) is supplied onto each susceptor 63 at a start point 71 of an upper forward path 41. A reaction gas 43A blown from a dispersion head 43 hits the semiconductor wafer heated by a heater 47 to form a predetermined thin film on the surface of the semiconductor wafer. This semiconductor wafer is removed from the susceptor 63 at an end point 72 of the forward path.
The susceptor 63 from which the semiconductor wafer is removed is cleaned through a lower return path 42, together with the endless belt 45 on which the susceptor 63 is fixed. In this cleaning operation, the susceptor 63 passes through an etching bath 48 coupled with a filter 51 and a pump 52 to remove the thin film grown on the surface of the susceptor 63 with an etching solution 49, such as hydrofluoric acid, filled in the etching bath 48. Then, the susceptor 63 passes through a water-cleaning bath 54 coupled with a pure-water inlet pipe 53 and having an overflow drain port 56 and cleaned with pure water 55 filled in the bath. The susceptor 63 is dried by a hot-air fan 57, then returns to the forward path 41, and is supplied with a new semiconductor wafer at the start point.
According to this method, the waiting periods for temperature drop and temperature rise to exchange a cleaned susceptor can be eliminated.
In the system of rotating the endless belt 45 on which the susceptors 63 are fixed, however, since the endless belt 45 itself serving as a means for moving the susceptors 63 is inevitably etched in etching for cleaning the susceptors 63, the material and the like of the endless belt 45 must be taken into special consideration. In addition, since the endless belt 45 is constituted by physically connecting rigid members so as to form a chain, the exchange operation and the like become difficult.
When one or a plurality of damaged susceptors 63 fixed to the endless belt 45 are to be exchanged, rotation of the endless belt 45 must be stopped, the damaged susceptors 63 must be dismounted from the endless belt 45, and then new susceptors must be attached and fixed, resulting in cumbersome maintenance.
As shown in FIG. 3, use of wet etching requires the etching bath 48, the water-cleaning bath 54, and the hot-air fan 57 serving as a drying means, increasing the size of the whole apparatus. On the other hand, if the apparatus is downsized to avoid this increase in size, the moving speed of the endless belt 45 must be decreased to perform etching, cleaning with water, and drying for a required period, decreasing the operating efficiency by CVD. In wet etching using this endless belt 45, since the etching solution enters the chain mechanism of the endless belt 45 cannot be removed by cleaning with water, this etching solution adversely affects subsequent formation of a thin CVD film.